[llvm-branch-commits] [llvm] [TBAA] Only clear TBAAStruct if field can be extracted. (PR #81285)

[Florian Hahn via llvm-branch-commits]

https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/81285

Retain TBAAStruct if we fail to match the access to a single field. All users at the moment use this when using the full size of the original access. SROA also retains the original TBAAStruct when accessing parts at offset 0.

Motivation for this and follow-on patches is to improve codegen for libc++, where using memcpy limits optimizations, like vectorization for code iteration over std::vector<std::complex<float>>: https://godbolt.org/z/f3vqYos3c

Depends on https://github.com/llvm/llvm-project/pull/81284

>From 99cf032dfabb21b820559bae61d2354e56336fdd Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Fri, 9 Feb 2024 16:25:32 +0000
Subject: [PATCH] [TBAA] Only clear TBAAStruct if field can be extracted.

Retain TBAAStruct if we fail to match the access to a single field. All
users at the moment use this when using the full size of the original
access. SROA also retains the original TBAAStruct when accessing parts
at offset 0.

Motivation for this and follow-on patches is to improve codegen for
libc++, where using memcpy limits optimizations, like vectorization for
code iteration over std::vector<std::complex<float>>:
https://godbolt.org/z/f3vqYos3c

Depends on https://github.com/llvm/llvm-project/pull/81284
---
 llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp           | 8 +++++---
 llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll | 5 +++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
index edc08cde686f1f..bfd70414c0340c 100644
--- a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -821,13 +821,15 @@ MDNode *AAMDNodes::extendToTBAA(MDNode *MD, ssize_t Len) {
 AAMDNodes AAMDNodes::adjustForAccess(unsigned AccessSize) {
   AAMDNodes New = *this;
   MDNode *M = New.TBAAStruct;
-  New.TBAAStruct = nullptr;
   if (M && M->getNumOperands() == 3 && M->getOperand(0) &&
       mdconst::hasa<ConstantInt>(M->getOperand(0)) &&
       mdconst::extract<ConstantInt>(M->getOperand(0))->isZero() &&
       M->getOperand(1) && mdconst::hasa<ConstantInt>(M->getOperand(1)) &&
-      mdconst::extract<ConstantInt>(M->getOperand(1))->getValue() == AccessSize &&
-      M->getOperand(2) && isa<MDNode>(M->getOperand(2)))
+      mdconst::extract<ConstantInt>(M->getOperand(1))->getValue() ==
+          AccessSize &&
+      M->getOperand(2) && isa<MDNode>(M->getOperand(2))) {
+    New.TBAAStruct = nullptr;
     New.TBAA = cast<MDNode>(M->getOperand(2));
+  }
   return New;
 }
diff --git a/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll b/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll
index 1042c413fbb7bb..996d2c0e67e165 100644
--- a/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll
+++ b/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll
@@ -38,8 +38,8 @@ define ptr @test2() {
 define void @test3_multiple_fields(ptr nocapture %a, ptr nocapture %b) {
 ; CHECK-LABEL: @test3_multiple_fields(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = load i64, ptr [[B:%.*]], align 4
-; CHECK-NEXT:    store i64 [[TMP0]], ptr [[A:%.*]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = load i64, ptr [[B:%.*]], align 4, !tbaa.struct [[TBAA_STRUCT3:![0-9]+]]
+; CHECK-NEXT:    store i64 [[TMP0]], ptr [[A:%.*]], align 4, !tbaa.struct [[TBAA_STRUCT3]]
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -86,4 +86,5 @@ entry:
 ; CHECK: [[TBAA0]] = !{[[META1:![0-9]+]], [[META1]], i64 0}
 ; CHECK: [[META1]] = !{!"float", [[META2:![0-9]+]]}
 ; CHECK: [[META2]] = !{!"Simple C/C++ TBAA"}
+; CHECK: [[TBAA_STRUCT3]] = !{i64 0, i64 4, [[TBAA0]], i64 4, i64 4, [[TBAA0]]}
 ;.